When

When Outlook starts a message box opens with the error:

"An add-in could not be found or could not be loaded

Customization could not be loaded because the application domain could not be created.
****** Exception Text ********
Microsoft.visualstudio.tools.applications.runtime.cannotcreatecustomizationdomainexception:
Customization could not be loaded because the application domain could not be created. --->
System.IO.FileLoadExpection: Could not load file or assembly ' PronestorOutlook2007AddIn, Version=3.1.4.0, Culture=neutral, PublickeyToken=385261ab4bd023d7' or one of its dependencies. The located assembly's manifest definition does not match the assembly...."

Or 

"the managed add-in loader failed to initialized"

Why

You have tried to install a new version of the add-in for PRONESTOR BOOKING for Outlook before uninstalling the existing

Or the pre-requisites are corrupt - and therefore require a reinstall

How to solve

Uninstall current before installing new add-in

Or

The VSTO is available as download from Microsoft at : http://www.microsoft.com/en-us/download/details.aspx?id=42513 

The PIA is available as download from Microsoft at: http://www.microsoft.com/en-us/download/details.aspx?id=3508